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THE BASIC-BESSEMER PROCESS. 119
CaS, while in the cinder from hot charges there will sometimes be from 30 to 40 per cent, less weight of phosphorus than was present in the pig-iron, although a cold hlow will show the full amount. On the other hand, Stead* gives the figures for a basic charge where all the sulphur that was lost by the metal appeared in the final slag. The analyses and summary are given in Table VII-C.
It will be noted that the calculation rests on "the probable weight of liquid slag" for one heat, and this can hardly be considered a conclusive proof that volatilization cannot occur, or that it does not often occur, or even that it does not usually occur. In another chapter (see Sec. Xlk) I have tried to show that such loss of sulphur may take place in open-hearth practice, and, if this is true, it seems probable that it will also hold good in the converter.
Some years ago it was the practice at two different works in Germany to add two-thirds of the lime at the beginning, so that when the metal was nearly dephosphorized the slag could be decanted, after which the rest of the lime could be put in and the final dephosphorization effected by a purer slag. The first cinder, which was rich in phosphorus and poor in iron, was fit for agricul-tur'al purposes, while the second, poorer in phosphorus and richer in iron, was used in the -blast furnace.
This practice has been discontinued and at all works the total quantity of lime is added at the beginning of the blow. The final slag runs as follows, in per cent.: Si02, 5 to 6; CaO, 45 to 50; PA, 16 to 20; PeO, 1.1 to 13; MnO, 5 to 6; MgO, 5 to 6, In some cases the Si02 may be higher, but the P205 is then in a less soluble state, and the slag is not so well suited for agricultural purposes.
SEC. VIII—Calorific equation.—The calorific equation of the basic converter may be calculated by the same method that was used in the work on the acid process (see Table VI-F), but the great quantity of slag and the absorption of heat in its liquefaction render accurate results rather hard to obtain. The silicon is lower in the pig-iron, and consequently the heat derived from this source is less, but the phosphorus more than makes up for the decrease. In the calculation in Section Vlf the net value of silicon per kg. was 4686 calories; of iron 741 cals.; of carbon 1163 cals., and, by the same method, we find that the value of phosphorus is 3821
* 0)v the Elimination of SulpJvur from Iron. Journal J, and S. I. "Vol. 1,1893, p. 61.